Typically, resins are petroleum by-products that have potentially very harmful burning characteristics, i.e., high flammability at relatively low temperatures, very toxic and acrid smoke, and rapid destructive flame spread. It is well known in the art that the flammability of curable resins can be reduced by incorporation of flame retardant agents. However, when additives are intended for use with curable resins, a multitude of problems arise.
Curable resins are frequently used in the manufacture of reinforced plastics, fiberglass laminates, reenforced plastics used as plenums and cable trays used for housing electrical wiring. Plastics are also widely used by automobile and aircraft manufacturers. The burning behavior of such materials, particularly those that are to be used in an enclosed situation, are of primary concern. Many reinforced plastics can be designed to have a degree of fire resistance. Many additives are available which inhibit burning, but unfortunately, many of these compounds give off very toxic fumes, such as nitrous oxides, cyanide, halogenated compounds etc.
Many prior art references describe the use of a variety of flame retardant additives, see “Modern Plastics Encyclopedia,” Vol. 63, No. 10A, McGraw-Hill, Inc., pp. 179-180 (1986). Typical flame retardant agents include reactive or additive halogenated organic compounds, inorganic fillers, solvents, and special formulations based on phosphorous and ammonium salts.
However, the selection of a suitable smoke suppressant for a curable resins is not predictable. Selection is particularly difficult when flame retardants are employed, exacerbated by the complex interaction between the resin and the flame retardant agent. Although efficient in suppressing the rate of combustion of finished products that incorporate the resin, most flame retardants tend to affect adversely one or more key properties of the resin. For example, many flame retardant additives are ineffective at producing low density and low toxicity formulations.
It is well known, that the flame retardant and smoke suppressive properties of additives in resin formulations varies greatly with the nature of substrate. This is particularly true for intumescent compositions because the rapid formation of a protective char is highly dependent upon such factors as the combustion temperature, and the viscosity of the melt formed by the burning substrate.
Other considerations can also come into play, even where the properties of the retardant and suppressive properties of the composition are optimum. These considerations include the effect of the additive on the physical properties, color and molding characteristics of the base resin.
U.S. Pat. No. 3,293,327 describes the production of bicyclic phosphites, phosphonates, thiophosphates, and selenophosphates. These compositions are said to be stabilizers for vinyl halide resins. They are said to be useful as heat stabilizers for vinyl chloride resin, and as antioxidants for fats and oils.
Intumescent, fire-retardant coating compositions containing carbonifics, film-forming binders and phosphorous materials are well known in the art. U.S. Pat. Nos. 3,562,197; 3,513,114; 4,009,137; 4,166,743 and 4,247,435 disclose such compositions containing ammonium polyphosphates as the phosphorous containing material.
U.S. Pat. No. 3,654,190 discloses an intumescent paint comprising a resinous binder, a blowing agent, a phosphorous containing material, a source of chlorine a solvent, an anti-settling agent, a pigment and a surfactant.
U.S. Pat. No. 3,969,291 describes the use of an amide polyphosphate condensate as a fire-retardant additive in an intumescent coating composition. U.S. Pat. No. 3,914,193 discloses the similar use of a crystalline form of melamine pyrophosphate.
U.S. Pat. No. 4,801,625, describe a flame resistant composition having (1) an organic polymeric substance in intimate contact with (2) a bicyclic phosphorous compound, and (3) a gas producing compound. The patent is silent on the use of bicyclic compounds to attain smoke suppressed flame retardant thermoset compositions.
U.S. Pat. No. 5,356,568 describes a solvent-based heat-resistant and fire-retardant coating containing carbonifics, film-forming binders, phosphorous materials. Also described is an application where the coating sprayed on steel and aluminum plates using a gravity flow gun. Not described are any smoke retardant properties, nor the use of the coating with resins or polymer plastics.
The development of additives for use with resins remains a highly empirical art. The predictability of the behavior of the final composition is rare to non-existent. The prior art has largely concentrated on developing highly specific additive combinations for particular resins and end-uses.
Therefore, it is desired to provided an additive composition which exhibits a greater latitude in dispersability, flame retardation, and smoke suppression. It is also desired to provide an additive for use in a variety of resins.